THE SPINAL CORD AS A CONDUCTING PATH 



605 



the arms and legs arise from the lower cervical and lower lumbar regions respec- 

 tively. It is for this reason that these particular segments of the cord are some- 

 what broader than the others, and present an elliptical outline, whereas the dorsal 

 region is almost circular. 



In cross-section the spinal cord is found to be composed of a central mass of 

 gray matter which is surrounded on all sides by a shell of white matter. The 

 former appears on each side in the form of a crescent, the convex surface of which 

 is turned inward and is joined with the one in the opposite half of the cord by a 

 transverse band or commissure. The entire mass of gray matter roughly exhibits 

 the shape of the letter H, and is divided on each side into an anterior or ventral 

 and a posterior or dorsal horn, the intervening substance being known as the 

 intermediate gray matter. The anterior horn is short and bulky, while the 

 posterior horn is narrow and slender, extending to the surface of the cord where it 



Dorsal median septum 



Septum 

 Dorsal lateral groove 



Dorsal nerve root 



Substantia gelatinosa 



Root-fibers entering 

 gray matter 



Processus reticularis 

 Central canal 



Nucleus from whic 

 motor fibers for mus- 

 cles of upper limb arise 



Ventral white commis- 

 sure 



Ventral nerve root 

 Ventral median fissure 



FIG. 297. CROSS-SECTION THROUGH THE HUMAN SPINAL CORD AT THE LEVEL OF THE 

 FIFTH CERVICAL NERVE, STAINED BY THE METHOD OF WEIGERT-PAL, WHICH COLORS THE 

 WHITE MATTER DARK AND LEAVES THE GRAY MATTER UNCOLORED. (From Cunning- 

 ham's Anatomy.) 



is invested by the substantia gelatinosa. The latter is known as the caput cornu 

 posterioris. In the lower cervical and thoracic regions, the intermediate gray 

 matter becomes unusually prominent and forms here the so-called lateral horn. 

 The center of the commissure uniting the right and left halves of the gray matter, 

 is occupied by a canal (0.5-1.0 mm. in diameter) which extends throughout the 

 entire length of the cord, and eventually communicates with the lymphatic spaces 

 of the brain. This is the remains of the primitive neural canal of the embryo. 

 It is surrounded by substantia gelatinosa and its walls are lined with cylindrical 

 epithelium. It is filled with liquor spinalis, a lymphatic fluid of the same char- 

 acter as the liquor contained in the cerebral spaces. 



The white matter of the spinal cord is made up of different bundles of sensory 

 and motor fibers which are arranged in such a way that they fill in the different 

 spaces externally to the gray matter. They are medullated, but possess no 

 neurolemma and run within tubes formed by the supporting neuroglia tissue. In- 

 asmuch as the entire mass of the spinal cord is divided into two halves by the ante- 

 rior and posterior median fissures, the white matter of each side presents itself in 



